Advances in Soil Science is a review series relevant to all areas of soil science. These reviews, intended primarily for scientists, teachers, and students of soil science, also provide technical background information for many additional workers and groups interested in our natural resources and man's influence on them. This is the eighth volume in the series with an international list of contributors from the United States, India, Canada and New Zealand. It contains four review chapters on the following subjects: factors affecting aluminum transformations in soil; soil productivity in dryland regions of developing countries; changes in soil structure under different cropping systems; properties and management of the depleted soils of India. These contributions present valuable information on a diversity of topics and serve as an excellent source of references.

From the beginning of agriculture until about 1950, increased food production came almost entirely from expanding the cropland base. Since 1950, however, the yield per unit of land area for major crops has increased dramatically. Much of the increase in yields was because of increased inputs of energy. Between 1950 and 1985, the farm tractor fleet quadrupled, world irrigated area tripled, and use of fertilizer increased ninefold. Between 1950 and 1985, the total energy used in world agriculture increased 6. 9 times. Irrigation played a particularly important role in the rapid increase in food production between 1950 and 1985. The world's irrigated land in 1950 totaled 94 million hectares but increased to 140 million by 1960, to 198 million by 1970, and to 271 million hectares in 1985. However, the current rate of expansion has slowed to less than 1 % per year. The world population continues to increase and agricultural production by the year 2000 will have to be 50 to 60% greater than in 1980 to meet demands. This continued demand for food and fiber, coupled with the sharp decline in the growth rate of irrigation development, means that much of the additional agricultural production in future years must come from cultivated land that is not irrigated. Agricultural production will be expanded in the arid and semiarid regions because these regions make up vast areas in developing countries where populations are rapidly rising.

Transboundary Policy Challenges in the Pacific Border Regions of North America responds to a growing interest in borderlands environmental policy by highlighting significant transboundary research and practices being undertaken within and across the Pacific border regions of North America. The issues explored here reveal how intricate and interrelated social, economic, and environmental concerns have become, particularly along borders, as Canada, Mexico, and the United States collectively search for sustainable solutions. Growing concern about the seriousness of environmental problems, particularly in high-growth border areas, coupled with the rising awareness of the complexities entailed in wise development decisions, has spurred recognition that new realities require new responses. Critical for effective environmental protection, restoration, and education is a sharing of understanding and effort across borders. Transboundary Policy Challenges in the Pacific Border Regions of North America highlights advances in transborder environmental research and discusses sensible policy directions with particular focus on critical areas of international concern and engagement: land and water use planning; regional growth management; trade and transportation corridors; environmental education; and travel and tourism. With Contributions By: J.C. Day Donald K. Alper K.S. Calbick Jose Luis Castru-Ruiz Alejandro Diaz-Bautista David A. Fraser Salvador Garcia-Martinez Warren G. Gill Duncan Knowler James Louckey Krista Martinez Martin Medina Jean O. Melious Cristobal Mendoza John C. Miles John M. Munroe Emma Spencer Norman Hugh O'Reilly Vicente Sanchez-Munguia Preston L. Schiller Tina Symko Peter Williams